The present invention relates generally to a level sensing system for use with an excavating machine in which a laser light beam provides a reference and, more particularly, to such a level sensing system arranged to assist the operator of the excavating machine in digging at a defined depth.
Use of laser reference systems for measurement and for machine control has become common in the construction industry. For example, a laser transmitter at a construction site is used to project a beam of laser light. The transmitter is designed to rotate the beam rapidly about a vertical axis. The rotating beam may be detected by laser beam receivers as a part of the process of surveying the construction site. The rotating beam defines a reference plane of light that can also be sensed by sensors mounted on various excavating machines and used to control the operation of those machines. The term excavating machines will be used herein to refer to equipment for performing digging operations, including for example graders, scrapers, trenchers, backhoes and excavators. Due to their similar structures (i.e., an outreach boom, pivotally connected to the machine chassis, a down reaching boom or dipper stick, pivotally connected to the distal end of the outreach boom, and a bucket pivotally connected to the distal end of the dipper stick), the digging stroke of such an excavating machine involves an arcuate movement of the dipper stick.
It will be appreciated that it will be difficult for a machine operator to use an excavating machine of this type to dig an area having a flat excavation surface. Further, digging to a desired depth over a larger area is also difficult with such an excavating machine and may require frequent measurement and adjustment in the depth of the excavation.
One approach to applying laser control to an excavating machine, for example a backhoe, is disclosed in U.S. Pat. No. 4,231,700, issued Nov. 4, 1980, to Studebaker. The Studebaker system does not attempt to limit movement of the bucket to a planar stroke. Rather, the disclosed apparatus includes a beam detector, mounted on a down reach boom, which is kept in a fixed relationship with respect to a reference plane defined by a rotating laser beam. Although the detector is maintained at a fixed height, the cutting edge of the backhoe falls and rises during the digging stroke due to the pivoting action of the down reach boom. Thus, the bottom of a trench which is dug utilizing this system will not be completely flat.
U.S. Pat. No. 4,393,606, issued Jul. 19, 1983, to Warnecke shows an excavator having a sensor supported by a mast which is mounted on the upper part of the bucket. A disadvantage of the Warnecke system is that in an excavation of any depth, the laser source must be placed in the excavation. This makes the Wameke system readily susceptible to damage during the normal course of an excavation. U.S. Pat. No. 4,888,890, issued Dec. 26, 1989, to Studebaker et al shows an excavator system in which the laser detector is supported on a mast that is held vertical by a counterweight. The mast is mounted at the pivotal connection between the outreach boom and the dipper stick, and the angular orientation of the dipper stick is determined by an inclinometer. Based on the detected vertical location of the laser beam and on the angular orientation of the dipper stick it is possible to calculate the vertical position of the bottom of the dipper stick and the bucket which it carries. Similarly, U.S. Pat. No. 6,263,595, issued Jul. 24, 2001, to Ake discloses a laser system for an excavator in which, in one embodiment, the dipper stick carries both a laser beam receiver and an inclinometer. The difficulty with an arrangement incorporating an inclinometer as shown in the Studebaker et al and Ake is that it is sensitive to vibration and motion induced errors. Essentially, in order to obtain an accurate reading of inclination, movement of the dipper stick must be temporarily stopped. Such an arrangement hampers operation of the excavator to an unacceptable degree.
It is seen therefore that there is a need for a simple level sensing system for use with an excavating machine in which accurate measurements may be made during operation of the machine without motion induced error.
This need is met by the present invention by providing a method and apparatus for controlling the working depth of a bucket of an excavating machine in response to a beam of laser light which is projected at a reference height. The level sensing system is used with an excavating machine of the type having a chassis, a boom pivotally secured to the chassis at a first pivot joint, a dipper stick pivotally secured to the boom at a second pivot joint, and a bucket pivotally secured to the dipper stick at a third pivot joint. The level sensing system includes a light receiving sensor, an inclinometer, and a position determining circuit. The light receiving sensor is mounted on the dipper stick and provides an indication of the relative location of a beam of light striking the light receiving sensor. The inclinometer is mounted on the dipper stick and provides an indication of the inclination of the dipper stick. The inclinometer includes a gyroscopic inclination sensor and an accelerometer arrangement for sensing acceleration due to gravity and providing a static vertical reference. The position determining circuit is responsive to the sensor and the inclinometer and calculates the position of the third pivot joint based on the inclination of the dipper stick and on the relative location of the beam of light striking the light receiving sensor.
The beam of light may be a beam of laser light which is projected by a laser transmitter and rotated to define a reference plane of laser light. The light receiving sensor may comprise an elongated photocell structure that is responsive to laser light and that provides a linear indication of the relative location of the beam to the position determining circuit.
The level sensing system may further comprise at least one angle-measuring sensor for measuring the angular orientation between the dipstick and a cutting edge of the bucket. The angle-measuring sensor provides an indication of the angular orientation to the position determining circuit, permitting the circuit to determine the location of the cutting edge of the bucket.
A level sensing system for use on a digging machine includes a light receiving sensor, mounted on a machine element, and providing an indication of the location of reference light striking the sensor. The location is a predetermined distance above a digging elevation. The light receiving sensor includes an elongated photocell arrangement. The system has a gyroscopic inclinometer mounted on the machine element. The inclinometer has at least one accelerometer that compensates for long term drift. Finally, the system has a circuit for calculating the position of a point on the machine element based on the location of the light striking the sensor and on the inclination of the machine element, as indicated by the inclinometer. The digging may be effected at the digging elevation by means of a digging element secured to the machine element at the point.
The machine element may typically be a dipper stick. The digging element may be a bucket that is pivotally mounted at the point on the dipper stick. An angle-measuring sensor provides an indication of the angle between the dipper stick and the bucket. The circuit is responsive to the angle-measuring sensor for determining the location of a cutting edge of the bucket.
Accordingly, it is an object of the present invention to provide a level sensing system for use with an excavator machine in which senses a reference plane of laser light and the angular orientation of a dipper stick to determine the vertical position of a the cutting edge of a bucket; to such a system in which an angular measurement is made between the dipper stick and the bucket; and to such a system in which the orientation is determined by a gyroscopic inclinometer including an accelerometer to correct for long term drift.